Long term carbon storage potential and CO2 sink strength of a restored salt marsh in New Jersey

Abstract

The study compares the amounts of carbon fixed via photosynthesis of a restored tidal marsh to the total organic carbon remaining in sediments of a natural tidal marsh and arrives at preliminary baselines for carbon sequestration and storage over time. The Eddy-covariance method (indirect method) was used to estimate marsh canopy net ecosystem exchange (NEE) and measured an annual gross primary production of 979gCm−2, while the loss through respiration was 766gCm−2, resulting in a net uptake of 213gCm−2yr−1. Time of the day, solar irradiation, air temperature, humidity and wind direction all together explained 66% of the variation in NEE. The high marsh community of Spartina patens showed NEE to be significantly higher than the low marsh community. The net ecosystem carbon balance (NECB) over long time scales was estimated by measuring the actual amount of total organic carbon contained in dated sediment cores from a natural marsh (direct method), which resulted in a carbon accumulation rate of 192.2gm−2yr−1. Changes in total organic carbon content over time in the core sample showed that 78% of organic carbon remained stored in the sediments after 130 years and only the most recalcitrant carbon (50%) remained under storage beyond 645 years. Overall the study showed that temperate macrotidal salt marshes are net sinks of carbon with potential for long term carbon storage. The marsh turned into a carbon sink at the beginning of May and switched back to being a source in late November. The average sedimentation rate estimated from the 137 CS dating (1950s to present) was 1.4mmyr−1 which is similar to accretion rates of comparable S. patens patches in the east coast. Accretion rates derived from our study are slightly lower than the 60+ year rate of sea level rise (2.6mmyr−1) recorded by tide gauge measurements in the Northeast.